Our understanding of the first seconds of our Universe’s existence is little more than an informed guess, based on inference and extrapolation. “Yet these first moments are the key to many of our most urgent and enduring cosmic mysteries,” cosmologist Dan Hooper at the University of Chicago told The Daily Galaxy. “Understanding this era,” he adds, “is essential to understanding our universe.”
In 2019, NASA selected a new space mission, SPHEREx, that will deliver an unprecedented map of the cosmos containing ‘fingerprints’ from the first moments in the universe’s history, said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate. “And we’ll have new clues to one of the greatest mysteries in science: What made the universe expand so quickly less than a nanosecond after the big bang?”
Search for the Essentials of Life
SPHEREx will survey hundreds of millions of galaxies near and far, some so distant their light has taken 10 billion years to reach Earth. In the Milky Way, the mission will also search for water and organic molecules – essentials for life, as we know it – in stellar nurseries, regions where stars are born from gas and dust, as well as disks around stars where new planets could be forming.
The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) mission is a planned two-year mission funded at $242 million (not including launch costs) and targeted to launch in 2024.
Measuring the Redshift of Hundreds of Millions of Galaxies
SPHEREx will survey the sky in optical as well as near-infrared light which, though not visible to the human eye, serves as a powerful tool for answering cosmic questions. Astronomers will use the mission to gather data on more than 300 million galaxies, as well as more than 100 million stars in our own Milky Way. Spherex will study the formation of water and other biogenic ices in the Milky Way to determine whether an exoplanet could harbor life.
“SPHEREx will use low-resolution spectroscopy to measure the redshift of hundreds of millions of galaxies,” Caltech physicist Jamie Bock, principal investigator of SPHEREx, wrote in an email to The Daily Galaxy. “The 3D distribution of these galaxies,” he explained, “can be used for tests of cosmology, such as studying the physical properties of dark energy. On large spatial scales variations in density reflect the primordial density waves set up by inflation. We plan to use SPHEREx measurements to probe inflation by studying ‘non-Gaussianity’ to new levels of accuracy. Possibly detectable levels of non-Gaussianity are predicted in certain models of inflation.”
Normal Distribution of Dark Matter or Asymmetries?
Some inflation models predict that the density distribution of dark matter shortly after the Big Bang should follow the popular bell-shaped symmetric curve called a Gaussian or normal distribution. Other inflation models instead suggest that slight asymmetries might exist, i.e., an overabundance of high-density and/or low-density regions relative to the Gaussian distribution. SPHEREx will observe a sufficiently large sample of high-redshift galaxies to measure very precisely the density distribution of matter in the early Universe, which can test these different inflation models.
Every six months, SPHEREx will survey the entire sky using technologies adapted from Earth satellites and Mars spacecraft. The mission will create a map of the entire sky in 96 different color bands, far exceeding the color resolution of previous all-sky maps. It also will identify targets for more detailed study by future missions, such as NASA’s James Webb Space Telescope and Wide Field Infrared Survey Telescope.
NASA’s Explorer program, managed by the agency’s Goddard Space Flight Center in Greenbelt, Maryland, has launched more than 90 missions, beginning in 1958 with Explorer 1, which discovered the Earth’s radiation belts. Another Explorer mission, the Cosmic Background Explorer, which launched in 1989, led to a Nobel Prize.
Caltech will work with NASA’s Jet Propulsion Laboratory to develop the mission payload. JPL will also manage the mission.